A micromanipulation technique was applied to measure the mechanical properties including the adhesive strength of Pseudomonas fluorescens biofilms grown in tubes. Using a T-shaped probe, a biofilm was deformed repeatedly to a small displacement, pulled and held, pulled and released at different speeds. The biofilm was finally pulled away from the surface to which it was attached. Simultaneously the force being imposed on the biofilm was measured. The adhesive strength between the biofilm and substratum was defined as the work required to remove the biofilm from the substratum per unit area. Results showed that the biofilms exhibited viscoelastic behaviour.